1. Field of the Invention
The present invention relates to the preparation of self-crimping polyester yarn having a high wind-up speed structure at low wind-up speeds, e.g., commercial POY (partially oriented yarn) speeds. More particularly, the present invention relates to the melt spinning of self-crimping polyester yarn wherein extruded polyester filamentary material having high and low shrinkage regions along its length is passed through an annealing or conditioning zone subsequent to the material being quenched through its glass transition temperature under conditions such that the resulting yarn maintains its self-crimping properties and has a high speed structure.
2. Description of the Prior Art
Polymeric filamentary materials and films have been produced in the past under a variety of melt extrusion conditions. For example, both high stress and low stress spinning processes have been employed. Under high stress conditions the as-spun filamentary material is withdrawn from the spinneret under conditions whereby substantial orientation is imparted to the material soon after it is extruded and prior to its complete solidification. See, for instance, U.S. Pat. Nos. 2,604,667 and 2,604,689. Such high stress conditions of the prior art commonly yield a non-uniform filamentary material wherein substantial radial non-homogeneity exists across the fiber diameter leading frequently to less than desired tensile properties, or even self-crimping characteristics.
Melt spinning processes have also been proposed wherein the cooling of the extruded filamentary material has been retarded (i.e., prolonged) prior to complete solidification so as to alter the properties thereof. See, for instance, U.S. Pat. Nos. 2,323,383; 3,053,611; 3,361,859; and 3,969,462. Note also Swiss Pat. No. 357,144.
Moreover, U.S. Pat. No. 3,946,100, of common assignee, discloses a process for producing polymeric filamentary material or film of improved tensile strength and modulus and diminished shrinkage characteristics, wherein a thermal conditioning zone is employed after solidification of the melt spun filamentary material, but prior to wind-up. In the process, molten melt-spinnable polymeric material capable of undergoing crystallization, such as a polyester, is extruded through a shaped orifice to form a filamentary material or film, quenched to below its glass transition temperature to form a solid filamentary material or film, and then passed for a brief residence time through a thermal conditioning zone at a temperature between its glass transition temperature and its melting temperature wherein substantial crystallization of the previously solidified filamentary material takes place under high stress conditions. The filamentary material is then withdrawn from the thermal conditioning zone. Thereby, the birefringence and tensile properties of the filamentary material are increased and improved so much so that a conventional hot drawing step may be unnecessary. U.S. Pat. No. 4,195,161, also of common assignee, more fully describes the unique polyester fiber which is obtained thereby. A similar process for melt spinning filaments is disclosed in German Offenlegungschrift No. 2,117,659.
See also European application Ser. No. 0,034,880 and the patents discussed therein regarding melt spinning processes employing a thermal conditioning zone provided with a gaseous atmosphere at a temperature above the glass transition temperature of the filamentary material but below its melting temperature, through which the solidified filamentary material is passed prior to wind-up.
U.S. Pat. No. 4,338,275 relates to a draw spinning process for the manufacture of filamentary polyester yarns at increased spinning speeds without significant deterioration in yarn properties. The process is one in which freshly extruded filaments are passed sequentially through a first fluid environment heated to a temperature above the melting point of the filaments and a second fluid environment heated to a temperature above the glass transition temperature of the filaments, with subsequent winding up of the filaments at a speed in excess of 5500 meters/minute. The two environments are separated from one another by a short distance, advantageously by between 100 cm and 500 cm, which distance is selected so that it is sufficient to cool the fibers below the temperature of the second fluid environment. The resulting yarns are comparable in properties with conventional spin-lag-draw hot relax yarns.
In Swiss Pat. No. 530,479, there is disclosed a method for making three-dimensional curled yarns and fibers by melt-spinning synthetic linear polymers and employing drawing speeds of over 2,000 m/min. The process steps comprise first chilling the melt spun filaments directly below the spinneret on only one side, and then completely cooling the filaments to the coagulation point or below. The cooled filaments are then heated to a temperature above the coagulation point prior to wind-up.
The melt extrusion of polymeric filamentary material, and in particular polyester filaments, under extrusion conditions such that a plurality of melt spun filaments are merged to thereby provide a self-crimping yarn has also been attempted in the prior art.
For example, Japanese Patent Publication No. 22339/1967 discloses extruding at low spinning speeds various polymers through combined orifices, each combined orifice including a large diameter central capillary and two or more small diameter satellite capillaries, the lengths of the various capillaries being unspecified. The spun yarns are then drawn under unspecified conditions to yield drawn filaments having cross-sectional shapes which vary continuously and cyclically along the length of each filament.
It has been found, however, that in practicing the aforedescribed process the draw ratio may need to be reduced to an unusual ratio before the crimp level in the relaxed yarn increases to a marginally useful level.
Japanese Patent Publication No. 42,415/1979 discloses spinning two polyester streams through a spinneret with converging capillaries wherein the streams intersect in midair (below the spinneret) to form a combined stream. One of the streams has a higher speed than the other, and an oscillation occurs in the molten stream such that the combined stream, when quenched into a filament, exhibits thick and thin regions along its length. When a number of these filaments are combined into a yarn and relaxed, a highly useful degree of crimp is obtained, and fabrics made from the yarn have an unusual soft, luxuriant hand.
In U.S. Pat. No. 4,332,758 there is disclosed a process for producing a self-crimping yarn comprising first and second types of filaments, said process comprising spinning the first type by forming a first plurality of molten polyester streams having recurring thick and thin regions out of phase from stream to stream; quenching the first plurality of streams into the first type of filaments having thick and thin regions along their lengths and out of phase from filament to filament; spinning the second type by extruding other streams of molten polymer of fiber-forming molecular weight from helical orifices selected to give filaments with helical cross-sections and lower shrinkages than the combined filaments at a given common spinning speed; and quenching the other streams into filaments; withdrawing the first and the second types of filaments from the streams at the common spinning speed; and combining the first and the second types of filaments into a yarn; the thick and thin regions in the first plurality of molten streams and the common spinning speed being selected such that the yarn has a crimp of at least 2%.
It is generally very difficult to manipulate the melt extrusion conditions used in extruding such self-crimping yarn, however, in order to alter and/or improve the properties of the yarn while maintaining a useful degree of crimp. For in such self-crimping yarn, the filaments have high and low shrinkage regions spaced, preferably regularly, along their length. The degree of shrinkage amplitude variation of the various regions is extremely important for obtaining a useful degree of crimp. For example, if the degree of shrinkage amplitude variations are too small, or if the shrinkage amplitude variations along the filaments are in phase, a useful degree of crimp would not be obtained. If a treatment, for example, a heat treatment, during the melt extrusion process does not effect the merged filaments in a correct proportional manner, the self-crimping characteristics of the resulting filament would thereby be lost. This ability to condition or alter the properties of such a self-crimping yarn without losing the yarn's useful self-crimping characteristics, i.e., for example, in obtaining a high speed yarn at much lower spinning speeds, would be most desirable and of a great advantage to the art. A process enabling the art to achieve and realize such benefits, however, has heretofore not been known.
Accordingly, it is an object of the present invention to provide a melt extrusion process which alters or modifies the characteristics of a self-crimping yarn without losing the useful self-crimping characteristics thereof.
Another object of the present invention is to provide a process for achieving high wind-up speed characteristics in a self-crimping yarn without losing the useful self-crimping characteristics of the yarn and without having to use high wind-up speeds.
Still another object of the present invention is to provide a process which effectively yields a self-crimping yarn having a higher level of amorphous orientation than is otherwise possible with conventional POY wind-up speeds.
These and other objects, as well as the scope, nature and utilization of the invention, will be apparant to those skilled in the art from the following description and appended claims.